Periodontal diseases continue to be a major cause of tooth loss in the adult human population. While advances in regenerative procedures proceed, the possibility of preventing these diseases remains most appealing. Of the many bacteria that comprise the periodontal microbiota, only a small number have been implicated in the initiation and progression of human periodontal diseases. Current research supports Porphyromonas gingivalis (Pg) as an etiologic agent of human periodontitis. The mechanisms by which Pg may initiate periodontitis or contribute to the tissue destruction characteristic of the disease are unknown at this time. We have identified and purified a cell surface-associated cysteine protease (lysyl endopeptidase) of Pg that also appears to be a fibrinogen and fibronectin binding protein. This M-r 150,000 protein is denoted FBP. In addition, we have cloned a fragment of Pg DNA which encodes a fibrinogen and fibronectin binding activity, and contains DNA that shares a high degree of sequence similarity with DNA encoding a portion of a hemagglutinin gene cloned from another strain of Pg. The experimental data obtained to date suggest that three putative virulence determinants of Pg, a lysyl endopeptidase activity, a fibrinogen and fibronectin binding activity and a hemagglutinating activity may be functions of the same Pg protein. This is an intriguing possibility and we propose to test this hypothesis. Alternatively, the ascribed FBP functions may be located on separate proteins that copurify. Three Specific Aims are proposed: 1) characterize the gene encoding the fibrinogen binding protein, fbp, and express the gene in E. coli, 2) determine if the functions ascribed to FBP can separated, and study structure/function relationships of the fbp gene product (FBP), 3) determine the substrate specificity of FBP and determine the similarity of this enzyme to other cysteine proteases. The results of this study will clarify the relationships between several putative virulence factors of Pg, will generate new information about what may be a novel multifunctional cell surface protease of Pg, and will provide insight into the catalytic mechanisms of cysteine proteases. Most importantly, information derived from these studies will not only provide new insights into the mechanisms of pathogenesis of Pg, but may also allow the design of highly selective therapeutic agents that could specifically interfere with single or multiple functions of FBP. Such agents may help achieve the long range goal of this research, which is to develop strategies to arrest the development of periodontitis early in the infectious process.